Our objectives are to obtain, by various approaches, information about the regulation of steroidogenic processes. Kinetic experiments have revealed that cholesterol is not the only sterol precursor of the steroid hormones. Esters of cholesterol (sulfate and organic acid esters) also serve as substrates for the cholesterol side-chain cleavage enzyme. Efforts to define better these steroidogenic systems and their regulations are being made. In addition, we have found that androstenedione is an obligatory intermediate in the placental conversion of dehydroisoandrosterone sulfate to estrone. The possibility that alternate pathways for the biosynthesis of estrogens exist is being tested. The regulation of adrenal microsomal 21-hydroxylase by constituents of the cytosol has been intensively studied. Several constituents of that fraction of the cell stimulate this enzyme. It is our intention to continue our efforts to establish more precisely how these and other factors control corticosteroidogenesis.